He said: “When we were out there in the calving grounds, with hundreds of thousands of females all giving birth at the same time, a very ­virulent disease swept through the population and killed around 150,000 of them in a matter of three days.

“At the time we thought we were watching the greatest natural catastrophe that I’d ever heard of. We watched 150,000 of these magnificent animals die in front of us.

“At the time we didn’t know if it was the final extinction of the species, which was devastating, emotionally, for the crew.”